The majority of the most widespread and discouraging of human cancers, including carcinoma of the lung, breast, colon and liver, are now known to display abnormalities in the protein products of the p53 tumor suppressor gene. It also seems likely that many if not most familial susceptibilities to cancers may turn out to be the consequence of inherited mutations in the p53 gene. The broad aim of this research is to gain new information about the biology of normal and mutant p53 tumor suppressor proteins, as its normal forms inhibit growth and as its mutant forms allow or promote malignant transformation. In this project period we will examine the hypothesis that p53 directly or indirectly exerts actions by altering the expression of other cellular genes. The approach will begin with the identification of the most immediate changes in cellular gene products (proteins and their mRNAs) that occur as the normal p53 protein inhibits growth, and as several mutant forms of p53 allow malignant change. To these ends we will utilize innovative ultra-high resolution methods developed in this laboratory to detect and quantify the cellular responses to several novel mutant-p53 expression vectors and temperature-sensitive p53 mutants developed in Arnold Levine's Laboratory (Princeton). Some constructs allow the regulated high-level expression of mutant (transforming) p53 molecules. Others are transforming mutants that shift their conformation to become normal growth-suppressing proteins at lower temperatures. We will then conduct sufficient studies on the circumstances associated with altered gene expression to select those proteins and messages that appear most directly responsive to p53. At that point we will undertake the molecular cloning of those that have the highest interest and study their structure and regulation. Finally, we anticipate the use of expression vectors to study the nature and functions of p53-responsive gene products, as related to the problem of malignant transformation in cultured cells, and in the context of their potential role as important determinants in the biology of cancer cells in humans. Our preliminary data indicates that we should be able to make substantial progress in these directions during this project period.